- 15% overall weight reduction, greater hull speed and reduced fuel consumption
- Cured shrinkage of less than 2% for epoxy resin, compared to 7-10% for PE and VE
- Injection time decreased from 1.5 hours to 45 minutes
Scout Boats Inc. has unveiled its much-anticipated 420 LXF model. The new model is the product of nearly three years of in-house research and development aimed at blending the performance of a fishing boat with the aesthetics of a high-end, centre-console cruiser. Contributing to the new design is the boat’s sleek, mirror-finish black hull, where Huntsman’s Araldite epoxy resins provided a strong bond and reduced the overall weight of the boat, resulting in greater hull speed and reduced fuel consumption.
When Scout Boats Inc. began considering the infusion process for the new hull, it decided on the process of building a vacuum-tight, flanged tool and infusing resins in a closed mold. As a result of this decision, a test programme was established for infusing a dark-coloured hard-top for a small boat using PE (Polyester), VE (Vinyl Ester) as well as epoxy resin supplied by Huntsman Advanced Materials. The goal: to compare the handling and cured performance of each material.
Major task: creating the black hull
One of the major tasks to be met during production was creating the black hull. It was acknowledged that this would be a challenge, as imperfections on this colour would be easy to notice. Fabrication with polyester resins often requires the addition of print blockers and barrier plies to prevent surface distortions and blemishes. Furthermore, completed hulls typically need time-consuming secondary rework and refinishing. The black 420 LXF epoxy-infused hull required little, if any, secondary finishing after demolding which significantly reduced labour time and improved the overall production speed.
Drawbacks of using PE and VE resins on dark-coloured parts
The hard-tops built for the test programme confirmed the drawbacks of using PE and VE resins on dark-coloured parts. By contrast, the epoxy resin, which has a cured shrinkage of less than 2%, compared to 7-10% for PE and VE, yielded blemish-free parts direct from the mold.
Epoxy resin is 20-30% stronger than PE and VE materials
The advantages of using epoxy went beyond the surface. Epoxy resin is 20-30% stronger than PE and VE materials with a higher elongation, tensile strength and modulus/stiffness properties. As a result, Scout was able to decrease the number of laminate layers without affecting strength and performance. Overall weight was reduced by 15% as well, providing for greater hull speed and reduced fuel consumption. The structurally sound, epoxy-infused hull would also resist osmotic weight gain from water absorption over time.
Production of the 420 LXF Hull
Scout built a vacuum-tight mold for the new hull using VE/fibreglass/core sandwich construction. To fabricate the hull, production began with a polyester gel coat backed by a fibre-filled vinylester skin coat. After sanding the skin coat, multiple plies of dry fibreglass, pre-cut according to a computer-designed laminate orientation schedule, lightweight, rigid foam core was then sandwiched between the fibreglass laminate layers. Next, a tackifier adhesive was sprayed over all plies to secure them in place until the epoxy is infused. To optimise the infusion process, a layer peel ply backed with external flow media was then put down.
To prepare for infusion, a disposable vacuum bag was installed, securing it tightly to mold flanges to eliminate air leaks. A series of resin infusion lines was then added with each line number-coded according to which area of the hull they will feed.
Resin system with water-like viscosity allows controlled resin flow throughout the laminate
Araldite LY 1568 / Aradur 3492 resin and hardener was mixed and infused using a high-feed MVP Patriot Pump. The resin system, specially formulated for use on large parts, has a water-like viscosity that accommodates controlled resin flow throughout the laminate. This ensures complete wet-out of reinforcing fabrics without resin-starved areas even in the notched sections of the stepped hull. After infusion, the epoxy cures at room temperature and is then post-cured under a tarp with a heat blanket that maintains a temperature of 71˚C (160˚F) for eight hours.
Epoxy resins post-cure at lower temperatures
Matthew Pogue, Commercial Representative at Huntsman Corporation elaborated, “Our new, advanced epoxy resins post-cure at lower temperatures than previously possible. Light-coloured parts can be cured at room temperature and yet still achieve high-quality results. As a result, energy costs are minimised while process control is maximised.”
As a further consequence of this, it was possible to reduce the number of infusion lines required and decrease injection time from 1.5 hours to 45 minutes. It was also noted that closed, infusion molding is faster than the previously used open-molding process. Scout is now able to produce each hull in less than a week and a completed boat every 3 to 3.5 weeks.
The company is already planning to build new 35-foot and 32-foot luxury fishing boats via infusion. Historically, the epoxy infusion process has widely been used by boat builders for single hull projects, but now Scout is leading the way for use of infusion for continuous production of boats by the marine industry.